Radioisotope Imaging Using γ-Ray Shadow Hologram

Abstract

Use of holography for imaging of radioisotope distribution which was reported by Barrett, H.H. in 1972, has been marked as a new γ-ray imaging. Generally in optical fields holography was very used for record and processing of three dimensional image by coherent wave such as laser beam. But γ-rays are incoherent and do not condense by optical lenses. So it was needed that the hologram of incoherent sources was formed without optical lenses. The method recording shadow of on axis zone plate with Fresnel diffraction pattern was used for obtaining an incoherent hologram. This method has the advantages of the improvements of resolution and γ-ray detection efficiency, and also the constitution of this system is simple and economical. But the disadvantage is that the process consists of two steps forming holograms and reconstructing images.
In this paper fundamental problems of γ-ray hologram and practicabilities for γ-ray imaging of this method were discussed.
In our system medical X-ray films combinating with industrial intensifying screens were used as a detector and γ-ray shadow holograms were obtained during about 3 minutes. From the shadow hologram, images were reconstructed using parallel beam of the laser (He-Ne laser, single mode, 6328Å, 1 mW) . Zone plate was consisted of coaxial lead rings with 10 open zones. The aperture area of this zone plate collimator was more several hundreds times than the pinhole, so the detection efficiency of γ-rays was better. Using ^99mTc 10 mCi as γ-ray source, points, English characters and thyroid phantom were tried to imaging and these reconstructed images were shown. Image resolution 3-5 mm was obtained in the reconstructed image of object at distance 10 cm from the collimator.